U.S. patent number 6,312,219 [Application Number 09/434,344] was granted by the patent office on 2001-11-06 for narrow waist vane.
This patent grant is currently assigned to General Electric Company. Invention is credited to John J. Decker, Mark J. Mielke, Kenneth E. Seitzer, Gregory T. Steinmetz, Peter J. Wood.
United States Patent |
6,312,219 |
Wood , et al. |
November 6, 2001 |
Narrow waist vane
Abstract
A compressor stator vane includes pressure and suction sides
extending chordally between leading and trailing edges, and
longitudinally between a root and a tip. The vane narrows in chord
to a waist between the root and tip. The vane may also be bowed at
its trailing edge in cooperation with the narrow waist.
Inventors: |
Wood; Peter J. (Cincinnati,
OH), Decker; John J. (Liberty Township, OH), Steinmetz;
Gregory T. (Cincinnati, OH), Mielke; Mark J.
(Blanchester, OH), Seitzer; Kenneth E. (Mason, OH) |
Assignee: |
General Electric Company
(Cincinnati, OH)
|
Family
ID: |
23723843 |
Appl.
No.: |
09/434,344 |
Filed: |
November 5, 1999 |
Current U.S.
Class: |
415/191;
416/223A |
Current CPC
Class: |
F01D
5/28 (20130101); F01D 5/141 (20130101); F04D
29/544 (20130101); F01D 5/282 (20130101); F01D
5/005 (20130101); F01D 5/284 (20130101); Y02T
50/60 (20130101); Y02T 50/673 (20130101) |
Current International
Class: |
F01D
5/14 (20060101); F04D 29/40 (20060101); F04D
29/54 (20060101); F01D 009/00 () |
Field of
Search: |
;415/191,192,208.1,208.2,210.1,193,194,195
;416/223R,223A,243,DIG.2,DIG.5,235,228 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Look; Edward K.
Assistant Examiner: McAleenan; James
Attorney, Agent or Firm: Hess; Andrew C. Young; Rodney
M.
Government Interests
The US Government may have certain rights in this invention
pursuant to Contract No. N00019-96-C-0176 awarded by the US
Department of the Navy.
Claims
Accordingly, what is desired to be secured by Letters Patent of the
United States is the invention as defined and differentiated in the
following claims in which we claim:
1. A compressor stator vane comprising pressure and suction sides
extending in a first plane chordally between leading and trailing
edges, and longitudinally between a root and tip, and narrowing in
chord to a waist therebetween, with said leading edge being
generally straight in an orthogonal second plane.
2. A vane according to claim 1 wherein said leading edge is tapered
toward said waist from said root and from said tip, and said waist
is generally concave at midspan in said first plane.
3. A vane according to claim 2 wherein said waist is disposed
within a range of about 30%-70% of longitudinal span from said
root.
4. A vane according to claim 3 wherein said waist is disposed at
about 50% span.
5. A vane according to claim 2 wherein said trailing edge is
generally straight longitudinally from said root to said tip in
said first plane.
6. A vane according to claim 5 wherein said trailing edge is
generally straight in both said pressure and suction sides.
7. A vane according to claim 6 narrowing in chord solely from said
leading edge, with said trailing edge being straight.
8. A vane according to claim 6 wherein said trailing edge is
configured to extend solely radially in axial elevation without
inclination with said leading edge in said first plane.
9. A vane according to claim 6 wherein said trailing edge is
inclined toward said leading edge from said root to tip in said
first plane.
10. A vane according to claim 9 wherein said trailing edge
inclination is constant from said root to said tip.
11. A vane according to claim 2 wherein said chords shorten to said
waist for effecting a substantially uniform diffusion loading
longitudinally from said root to tip.
12. A vane according to claim 2 wherein said suction side is bowed
at an obtuse angle between said trailing edge and each of said root
and tip in said second plane.
13. A vane according to claim 12 wherein said trailing edge is
generally straight in said pressure and suction sides in said first
plane and orthogonal to said bow of said suction side thereat in
said second plane.
14. A vane according to claim 12 wherein said obtuse angle is
within a range of about 110.degree.-130.degree..
15. A vane according to claim 12 wherein said chords shorten to
said waist for effecting a substantially uniform diffusion loading
longitudinally from said root to said tip.
16. A vane according to claim 12 wherein said leading edge is
substantially normal to said root and tip in said second plane.
17. A vane according to claim 16 wherein said leading edge is
generally straight between said root and tip in said second plane
and orthogonal to said taper thereof in said first plane.
18. A vane according to claim 16 wherein said obtuse angle
decreases in magnitude from said trailing edge toward said leading
edge.
19. A vane according to claim 12 further comprising an inner band
joined normal to said root in said second plane, and an outer band
joined normal to said tip in said second plane for effecting said
obtuse angle between said suction side at said trailing edge with
both said bands.
20. A compressor stator vane comprising:
pressure and suction sides extending in a first plane chordally
between leading and trailing edges, and longitudinally between a
root and tip, and narrowing in chord to a waist therebetween, with
said leading edge being generally straight in an orthogonal second
plane; and
said suction side is bowed at an obtuse angle between said trailing
edge and each of said root and tip in said second plane.
21. A vane according to claim 20 further comprising an inner band
joined normal to said root in said second plane, and an outer band
joined normal to said tip in said second plane for effecting said
obtuse angle between said suction side at said trailing edge with
both said bands.
22. A vane according to claim 21 wherein:
said chords narrow solely from said leading edge; and
said trailing edge is generally straight in said pressure and
suction sides in said first plane and orthogonal to said bow of
said suction side thereat in said second plane.
23. A vane according to claim 22 wherein said chords shorten to
said waist for effecting a substantially uniform diffusion loading
longitudinally from said root to tip.
24. A vane according to claim 22 wherein said waist is disposed
within a range of about 30%-70% of longitudinal span from said
root.
25. A vane according to claim 24 wherein said obtuse angle is
within a range of about 100.degree.-130.degree..
26. A vane according to claim 22 wherein said leading edge is
generally straight between said root and tip in said second plane
and orthogonal to said taper thereof in said first plane.
27. A compressor stator vane 18 comprising a scalloped leading edge
with a waist of minimum chord in a first plane, and a trailing edge
bowed orthogonally relative to said leading edge in an orthogonal
second plane.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to gas turbine engines,
and, more specifically, to compressors or fans therein.
In a turbofan aircraft gas turbine engine, air is pressurized in a
fan and compressor during operation. The fan air is used for
propelling an aircraft in flight. The air channeled through the
compressor is mixed with fuel in a combustor and ignited for
generated hot combustion gases which flow through turbine stages
that extract energy for powering the fan and compressor.
A typical turbofan engine includes a multistage axial flow
compressor which pressurizes the air sequentially to produce high
pressure air for combustion. The compressed air is diffused and
decelerates as it is compressed. Compressor airfoils must therefore
be designed to reduce undesirable flow separation which would
adversely affect stall margin and efficiency.
Conversely, combustion gases are accelerated through the turbine
stages, and the turbine blades have different aerodynamic designs
for maximizing efficiency of energy extraction.
Fundamental in compressor design is efficiency in compressing the
air with sufficient stall margin over the entire flight envelope of
operation from takeoff, cruise, and landing.
However, compressor efficiency and stall margin are normally
inversely related, with increasing efficiency typically
corresponding with decrease in stall margin. The conflicting
requirements of stall margin and efficiency are particularly
demanding in high performance military engine applications, as
opposed to less demanding commercial applications, which require
high level of stall margin typically at the expense of compressor
efficiency.
Maximizing efficiency of compressor airfoils is primarily effected
by optimizing the velocity distributions over the pressure and
suction sides of the airfoil. However, efficiency is typically
limited in conventional compressor design by the requirement for a
suitable stall margin. Any further increase in efficiency typically
results in a reduction in stall margin, and, conversely, further
increase in stall margin results in decrease in efficiency.
High efficiency is typically obtained by minimizing the wetted
surface area of the airfoils for a given stage to correspondingly
reduce airfoil drag. This is typically achieved by reducing airfoil
solidity or the density of airfoils around the circumference of a
rotor disk, or by increasing airfoil aspect ratio of the chord to
span lengths.
For a given rotor speed, this increase in efficiency reduces stall
margin. To achieve high levels of stall margin, a higher than
optimum level of solidity may be used, along with designing the
airfoils at below optimum incidence angles. This reduces axial flow
compressor efficiency.
Increased stall margin may also be obtained by increasing rotor
speed, but this in turn reduces efficiency by increasing the
airfoil Mach numbers, which increases airfoil drag.
Compressor performance is also affected by the cooperation of
compressor rotor blades and stator vanes. A row of blades extends
radially outwardly from a supporting rotor disk and rotates during
operation within a surrounding stator casing. A corresponding row
of stator vanes is disposed directly upstream from the blades for
controlling airflow thereto.
The stator vanes typically have radially outer tips mounted in an
annular outer band, and radially inner roots suitably mounted in a
radially inner band which typically supports an inner seal. Such
mounting is typically effected by stabbing the individual vanes
through complementary apertures in the bands, and securing the
vanes thereto by brazing or welding for example. The individual
vanes are typically straight and rigid for undergoing this
manufacturing process without distortion.
However, typical vanes have relatively uniform radial profiles from
root to tip and limit efficiency of operation and stall margin. The
bands define endwalls along which boundary layers of air form
during operation and affect performance. Aerodynamic or diffusion
loading of the vanes is higher near the endwalls than the midspan
regions of the vanes, and the vane-endwall interfaces are subject
to flow separation along the vane suction sides near the trailing
edges as the air diffuses during operation.
Accordingly, typical compressor design necessarily includes a
compromise between efficiency and stall margin favoring one over
the other. And, differences in blade and vane designs additionally
complicate compressor design. It is, therefore, desired to further
improve both compressor efficiency and stall margin by enhancing
compressor vanes and improving cooperation with corresponding
compressor blades.
BRIEF SUMMARY OF THE INVENTION
A compressor stator vane includes pressure and suction sides
extending chordally between leading and trailing edges, and
longitudinally between a root and a tip. The vane narrows in chord
to a waist between the root and tip. The vane may also be bowed at
its trailing edge in cooperation with the narrow waist.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, in accordance with preferred and exemplary
embodiments, together with further objects and advantages thereof,
is more particularly described in the following detailed
description taken in conjunction with the accompanying drawings in
which:
FIG. 1 is an axial sectional view through a portion of a gas
turbine engine compressor including a row of stator vanes disposed
axially between corresponding rows of rotor blades in accordance
with an exemplary embodiment of the present invention.
FIG. 2 is a radial sectional view through one of the compressor
vanes illustrated in FIG. 2 and taken along 2--2.
FIG. 3 is an axial, side elevational view, like FIG. 1, of the
compressor vanes in accordance with an alternate embodiment of the
present invention.
FIG. 4 is an upstream facing, isometric view of three adjacent
compressor vanes mounted in corresponding radially inner and outer
bands, and taken generally along line 4--4 in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Illustrated in side elevational view in FIG. 1 is a portion of a
gas turbine engine compressor 10 configured for channeling and
pressurizing air 12. The compressor is axisymmetrical about an
axial centerline axis 14 and includes multiple axial stages of
corresponding rotor blades 16 extending radially outwardly from
corresponding rotors in the form of separate disks, or integral
blisks, or annular drums in any conventional manner.
Cooperating with each rotor stage is a corresponding compressor
stator having a plurality of circumferentially spaced apart stator
vanes 18. The blade 16 and vanes 18 define airfoils having
corresponding aerodynamic profiles or contours for pressurizing the
air 12 successively in axial stages. In operation, pressure of the
air is increased as the air decelerates and diffuses in the axial
direction from stage to stage.
As shown in FIGS. 1 and 2, each stator vane 18 defines an airfoil
including a generally concave pressure side 20 and a
circumferentially opposite, generally convex suction side 22. The
two sides 20,22 extend chordally between an upstream leading edge
24 and an axially opposite, downstream trailing edge 26.
The individual vanes 18 may be defined relative to an orthogonal
coordinate system including an axial axis X extending parallel with
the engine centerline axis 14; a tangential or circumferentially
extending axis Y; and a radially extending axis Z. Each vane 18 may
therefore be defined by a plurality of radially stacked planar
sections extending radially outwardly from a root 28 and a tip 30
as shown in FIG. 1.
In the exemplary embodiment illustrated in FIG. 1, the row of vanes
18 is suitably supported in corresponding radially inner and outer
bands 32,34, with the inner band typically supporting a suitable
seal (not shown). The vane roots 28 and tips 30 are typically
fixedly mounted in complementary apertures in the corresponding
bands 32,34, with the bands defining endwalls which radially bound
the flow of air 12 between the adjacent vanes 18.
As indicated above, conventional compressor design typically
requires a compromise in compression efficiency and stall margin.
The airfoils of conventional compressor vanes are typically
radially similar due to two dimensional aerodynamic definition
thereof.
Modem computer software is now conventionally available for solving
three-dimensional (3D) viscous flow equations for more fully
evaluating airfoil performance. Such 3D software may be used for
designing both the rotor blade 16 and the stator vanes 18, with the
stator vanes being the subject of the present invention. The
resulting vane airfoils in accordance with the present invention
generally have distinctive 3D configurations which differ
significantly over conventional airfoils which vary little in
radial section over the longitudinal or radial spans thereof.
As initially shown in FIG. 2, each radial section of the vane 18 is
defined by the aerodynamic contour or profile along the pressure
and suction sides 20,22 extending between the leading and trailing
edges 24,26. Each section has a chord extending from leading to
trailing edge, and identified by its chord length C.
As shown in FIG. 1, and in accordance with an exemplary feature of
the present invention, the stator vane 18 narrows in chord to a
waist 36 of minimum chord length which is preferably disposed
centrally between the root 28 and tip 30 along the longitudinal or
radial span of the vane.
The leading edge 24 is preferably tapered toward the waist 36 from
both the root 28 and the tip 30, with a generally concave axial
side view or projection as illustrated in FIG. 1 defining a leading
edge having a single scallop. The waist 36 is preferably disposed
within a range of about 30%-70% of the longitudinal or radial span
of the vane from its root 28. In the preferred embodiment
illustrated, the waist 36 is disposed at about 50% span. And, the
waist 36 may be up to about 30% less than the root and tip
chords.
As shown in side view or axial projection in FIG. 1, the trailing
edge 26 is preferably generally straight longitudinally or radially
between the root and tip. In axial projection from either vane
side, the trailing edge 26 appears straight in both the pressure
and suction sides in the X-Z plane.
As further discussed hereinbelow, the stator vane 18 preferably
narrows in chord solely from the leading edge 24 toward the
trailing edge 26, with the trailing edge remaining straight in
axial profile. In the preferred embodiment, the trailing edge 26 is
configured to extend solely radially in axial elevation or
projection without inclination with the leading edge. In this way,
the waist 36 is defined solely by the tapered or scalloped leading
edge 24, with the trailing edge being straight radially and without
scallop.
By introducing the narrow waist 36 centrally in the vane by
reducing chord length from both endwalls, improved 3D performance
of the stator stage may be effected. The narrow midspan or central
portion of the vane has a corresponding reduction in wetted surface
area, and therefore aerodynamic drag is correspondingly
reduced.
Preferably, the vane narrows to its waist with a corresponding
shortening of the chords from both endwalls for effecting a
substantially uniform diffusion loading longitudinally or radially
from root 28 to tip 30. By defining the radial chord distribution
of the vane to achieve a substantially uniform aerodynamic loading
across the airfoil span, enhanced performance and efficiency may be
obtained, while eliminating the extra chord length near the vane
waist which is not required for efficient air compression.
The vane is selectively narrowed at the central waist to
correspondingly increase loading and diffusion thereat without
compromising loading and diffusion near the endwalls. The
longitudinal loading distribution may be substantially uniform as
indicated above, or may be slightly greater at vane midspan to
ensure a smooth chord distribution. Compression efficiency is
therefore increased by increasing diffusion in the vane central
region, while correspondingly decreasing drag thereat.
Furthermore, chord reduction is preferably effected at the front or
leading edge of the airfoil instead of the trailing edge to
increase aerodynamic sweep of the leading edge at the endwall
bands. Aerodynamic sweep is a conventional parameter and the
forward sweep effected at the vane leading edge near the inner and
outer bands 32-34 further improves aerodynamic performance of the
vane.
The scalloped leading edge 24 may also be effected with a straight
but inclined trailing edge. As shown in an alternate embodiment in
FIG. 3, the trailing edge 26 may remain straight in axial
projection but may be inclined toward the leading edge 24 from root
to tip at an acute inclination angle A which may be up to about
10.degree.. The inclination angle A is preferably constant between
the root and tip.
Compressor efficiency may be further increased, along with improved
stall margin, by further modifying the vanes 18 as illustrated in
tangential view or projection in the Y-Z plane illustrated in FIG.
4. The Y-Z plane illustrated in FIG. 4 is orthogonal or normal to
the X-Z plane illustrated in FIG. 1 for showing two projections of
the same vanes 18 corresponding with tangential and axial
projections, respectively.
As shown in FIG. 4, the vane suction side 22 is preferably bowed at
an obtuse angle B between the trailing edge 26 and each of the root
28 and tip 30. The trailing edge 26 also defines a lean angle D
with the radial axis in the tangential direction or view
illustrated.
Since the vanes 18 are configured to turn and diffuse the airflow
12, flow separation of the air is a design consideration primarily
on the vane suction side near the trailing edge. In a conventional,
generally radially straight stator vane, the vane suction side is
generally normal to the corresponding endwalls and is subject to
flow separation thereat. However, by bowing the suction side of the
vanes 18 illustrated in FIG. 4 along the trailing edges, the
resulting obtuse angles B can significantly reduce or eliminate
undesirable flow separation at the endwalls or bands.
Correspondingly, a further increase in compressor efficiency and
stall margin may be obtained therefrom.
In the axial end view illustrated in FIG. 4, the individual vanes
18 are bowed primarily along their trailing edges 26 to create
similar obtuse angles B at both the root 28 and tip 30. The lean
angle D correspondingly varies over the longitudinal span of the
vane to smoothly interconnect the oppositely inclined root and tip
portions at the trailing edge. Preferably, the lean angle varies
continuously between the root and tip.
The bowed trailing edge illustrated in FIG. 4 may be effected by
varying the corresponding camber and stagger angle of each radial
section, along with bowing the stacking axis 38 of the vane from a
radial line, primarily in the tangential component thereof. The
stacking axis for vanes is preferably the locus of mid-points of
the camber lines of individual radial vane sections, which
mid-points are typically radially aligned along the span of a vane.
In FIG. 4, the tangential component of the stacking axis 38 is
bowed and displaced from the radial span axis to effect the
preferred bowed trailing edge of the vane.
The scalloped leading edge 24 illustrated in FIG. 1 is preferably
used in combination with the bowed trailing edge 26 illustrated in
FIG. 4, preferably without one compromising the other. The
combination thereof further enhances aerodynamic efficiency, and
the reduction or elimination of undesirable flow separation at the
endwalls.
More specifically, the same vane 18 illustrated in FIGS. 1 and 4
preferably includes both the scalloped leading edge 24 with the
central waist 36 of minimum chord, and the trailing edge 26 bowed
orthogonally therefrom. As shown in FIG. 1, the trailing edge 26 is
generally straight in the axial projection of the pressure and
suction sides 20,22, as well as being bowed along the suction side
22 in the orthogonal tangential plane illustrated in FIG. 4. This
combination of the trailing edge 26 in two orthogonal planes
permits the amount of trailing edge lean D to be maximized, with a
substantially large obtuse angle B for further improving compressor
efficiency and stall margin.
The obtuse angle B may therefore be maximized within an exemplary
range of about 100.degree.-130.degree., with the 130.degree.
exemplary upper limit being chosen for manufacturing reasons as
discussed hereinbelow. The large trailing edge bow cooperates with
the scalloped leading edge with 3D synergy for maximizing the
uniformity of diffusion loading longitudinally from the vane root
28 to tip 30. Uniform aerodynamic loading is effected also with a
substantial reduction or elimination of flow separation between the
vane suction side and corresponding endwalls at the trailing
edge.
As shown in FIGS. 2 and 4, the vane leading edge 24 is preferably
substantially normal or perpendicular to the corresponding root 28
and tip 30 and extends primarily in the radial direction.
Furthermore, the leading edge 24 is generally straight at the root
and tip in the tangential plane illustrated in FIG. 4, which is
orthogonal to the taper of the leading edge in the axial plane
illustrated in FIG. 1.
Although the trailing edge portion of each vane is tangentially
bowed as discussed above, the leading edge portions of the vanes
are relatively straight for maintaining longitudinal rigidity of
the vanes for permitting their assembly with the corresponding
bands. Such assembly is typically effected by stabbing the
individual vanes into complementary apertures in the bands with
sufficient force to effect an interference fit therewith. The
individual vanes therefore require longitudinal stiffness to
prevent buckling or longitudinal distortion under the considerable
stabbing forces employed.
The obtuse interface angle B illustrated in FIG. 4 is preferred
locally at the vane trailing edge, and preferably decreases in
magnitude from the trailing edge toward the leading edge 24. At the
leading edge, the interface angle B approaches 90.degree.. In this
way, a significant portion of each vane may maintain a normal or
perpendicular orientation relative to its opposite root and tip for
maintaining radial stiffness thereof and permitting stabbing
assembly of the vanes with the bands. The bowing of each vane may
thusly be limited to the trailing edge region for enhancing
aerodynamic performance without compromising manufacturability.
The scalloped and bowed stator vanes 18 illustrated in FIG. 4
thusly enjoy improved aerodynamic performance with their supporting
bands 32,34. The obtuse interface angle B is effected between the
vane suction side 22 and the trailing edge 26 at both endwalls
32,34. Flow separation thereat is significantly reduced or
eliminated, and more uniform aerodynamic loading of the vanes
across their radial spans is effected for further improving
efficiency.
The scalloped and bowed features of the stator vanes may be used
separately or in combination for maximizing efficiency and stall
margin due to the synergistic combination thereof.
While there have been described herein what are considered to be
preferred and exemplary embodiments of the present invention, other
modifications of the invention shall be apparent to those skilled
in the art from the teachings herein, and it is, therefore, desired
to be secured in the appended claims all such modifications as fall
within the true spirit and scope of the invention.
* * * * *